This invention relates to a process for preparing a thermoplastic resin composition having excellent dimensional stability, heat resistance, impact resistance, solvent resistance and appearance of a molded product.
Non-crystalline thermoplastic resins for molding such as a polyphenylene ether (hereinafter referred to as "PPE") have been generally known as a polymer material or engineering plastics having excellent heat resistance, dimensional stability and electric characteristics, but there are drawbacks that some of them have bad melt fluidity (flowability when melting), whereby molding processing is difficult, and also solvent resistance and impact resistance are poor.
On the other hand, a crystalline thermoplastic resin such as a polyolefin and a saturated polyester has been generally used widely as a polymer material having excellent molding processability, solvent resistance and mechanical strength, low specific gravity and an inexpensive material in the fields of parts for automobiles and parts for electric and electronic equipments. However, the crystalline thermoplastic resin has drawbacks that molding shrinkage rate and linear expansion coefficient are high, and also rigidity is greatly lowered at high temperatures. In order to remove these drawbacks, there has been proposed a method of filling up a reinforcing agent such as glass fiber, but the method has a problem that appearance of a molded product is worsened so that application thereof is limited depending on the field.
If a composition having both good properties of the non-crystalline thermoplastic resin and the crystalline thermoplastic resin and compensating undesirable properties each other can be obtained, an excellent resin material having a wide application field can be provided, and it can be said that industrial significance of such a material is extremely great. Therefore, for the purpose of providing a molding material in which disadvantages of both resins are compensated each other without impairing advantages thereof, there have been proposed, for example, compositions in which a PPE which is a non-crystalline thermoplastic resin and a polyester which is a crystalline thermoplastic resin are simply melted and mixed in Japanese Patent Publication No. 21664/1976 and Japanese Provisional Patent Publications No. 50050/1974, No. 75662/1974 and No. 159847/1984, a composition in which a PPE and a polyamide which is a crystalline thermoplastic resin are simply melted and mixed in Japanese Patent Publication No. 41663/1984, and further a composition in which a PPE and a polyolefin which is a crystalline thermoplastic resin are simply melted and mixed in U.S. Pat. No. 3,361,851 and Japanese Patent Publication No. 7069/1967.
However, in such a simple blend system, the non-crystalline thermoplastic resin and the crystalline thermoplastic resin have inherently poor compatibility with each other so that adhesiveness at an interface of the two phase structure is not good, whereby two phases can hardly take uniform and fine forms. Therefore, when shear stress is applied during molding processing such as injection molding, laminar peeling (delamination) is easily caused, whereby appearance of a resulting molded product is worsened and an interface of two phases becomes a defective portion. Thus, it is impossible to obtain a composition having excellent mechanical characteristics such as impact resistance and rigidity and excellent physical characteristics such as solvent resistance.
Therefore, there have been proposed several techniques of improving compatibility of both resins. For example, in Japanese Provisional Patent Publications No. 218748/1988 and No. 40556/1989, it has been proposed that a specific block copolymer is added as a compatibilizing agent to a resin composition comprising a PPE and a polyolefin, and in Japanese Provisional Patent Publication No. 185553/1990, it has been proposed that polystyrene graft polypropylene is used in a resin composition comprising a PPE, a polyolefin and a rubbery substance. However, a resin composition which can satisfy utility in all points of heat resistance, rigidity, impact resistant strength, solvent resistance and moldability has not yet been obtained. Thus, improvement has been required. There have been also disclosed a method of using a modified PPE obtained by reacting a compound having both (i) a carbon-carbon double bond or a carbon-carbon triple bond and (ii) one or more selected from a carboxylic acid, an acid anhydride, an acid amide, an epoxy group and a hydroxyl group (Japanese Provisional Patent Publications No. 257958/1987 and No. 54427/1988 and PCT Provisional Patent Publication No. 500803/1988), a method of using an alkoxysilyl group-modified PPE (PCT Provisional Patent Publication No. 503392/1988), a method of using an oxazoline-modified PPE (Japanese Provisional Patent Publication No. 187453/1990), a method of using a polyester modified with a hydroxyl group or carboxyl group-terminated polystyrene (Japanese Provisional Patent Publication No. 170852/1990) and a method of formulating oxycarboxylic acids (Japanese Provisional Patent Publication No. 129259/-1990). However, even by using these methods, compatibility of PPE and the saturated polyester cannot be improved sufficiently in many cases, and it cannot be said that mechanical characteristics of resulting compositions are sufficient. Thus, further improvement has been demanded.